[AArch64][3/14] Refactor option override code

[AArch64][3/14] Refactor option override code

	* config/aarch64/aarch64.opt (aarch64_arch_string): Delete.
	(aarch64_cpu_string): Likewise.
	(aarch64_tune_string): Likewise.
	* config/aarch64/aarch64.c (aarch64_parse_opt_result): New enum.
	(aarch64_parse_extension): Return aarch64_parse_opt_result.
	Add extra argument to put result into.
	(aarch64_parse_arch): Likewise.  Do not set selected_cpu.
	(aarch64_parse_cpu): Add arguments to put results into. Return
	aarch64_parse_opt_result.
	(aarch64_parse_tune): Likewise.
	(aarch64_override_options_after_change_1): New function.
	(aarch64_override_options_internal): New function.
	(aarch64_validate_mcpu): Likewise.
	(aarch64_validate_march): Likewise.
	(aarch64_validate_mtune): Likewise.
	(aarch64_override_options): Update to reflect above changes.
	Move some logic into aarch64_override_options_internal.
	Initialize target_option_default_node and target_option_current_node.
	(aarch64_override_options_after_change): Move logic into
	aarch64_override_options_after_change_1 and call it with global_options.
	(initialize_aarch64_code_model): Take a gcc_options pointer and use the
	flag values from that.

	* gcc.target/aarch64/cpu-diagnostics-3.c: Update expected error
	message.

From-SVN: r226554